Philip III, in French Philippe III, surnamed "the Bold" (le Hardi), King of France, son of Louis IX and Margaret, daughter of Raymond-Bérenger IV, count of Provence, was born on the 3rd of April 1245. His funeral monument at St. Denis depicts a man with beardless, square-cut features, but lacking character and animation. The authenticity of this effigy is fairly well borne out by what is known of him from other sources. He had many of the virtues of his father St. Louis, but neither decision of character nor devotion to duty. He was pious, charitable, of unimpeachable morality, quick-tempered but placable, no great scholar, and only energetic as a hunter. The absence in him of the qualities that fit a man to rule made his court the arena of intriguing factions, which in reality ruled France during his reign of fifteen years. Matthew of Vendôme, abbot of St. Denis, an old servant of Louis IX, acted as Philip's counsellor, so the chroniclers state, throughout the reign; but he is only a shadowy figure, and it is difficult to reconcile the statement that "everything was done according to his will" with the known facts. It was probably with administration, and not policy, that Matthew was chiefly concerned. In one instance at least his advice was openly flouted. Coming to the throne by the death of his father on the 25th of August 1270, Philip began his reign by falling entirely under the influence of Pierre de la Brosse, who had been surgeon and valet-de-chambre to his father, upon whom he lavished lands and honors, making him lord (sieur) of Langeais, Chatillon-sur-Indre and Damville. Even King Edward I of England and William Dampierre, count of Flanders, strove to win his favor by gifts. But his fall was assured when Philip, who in 1271 lost his first wife. Isabella, daughter of James I, king of Aragon, married in 1274 Marie, daughter of Henry III, duke of Brabant. She was young and beautiful, and supplied a center around which those who wished the downfall of the favorite grouped themselves. In June 1278 he was charged with various crimes, including one of poisoning the king's eldest son, and hanged at Montfaucon. His death left the parties of Marie, the queen, and Margaret, the queen-mother, to struggle for the mastery. The first subject of dispute was the inheritance of the count of Provence, Raymond-Bérenger IV, father of Margaret and of Eleanor, wife of King Henry III of England. Upon his death, in 1245, his youngest daughter, Beatrice, wife of Charles of Anjou, the king's uncle, succeeded to his lands, to the exclusion of her elder sisters, who claimed some portion of them for themselves. In 1281 war nearly broke out on this question. Margaret and her friends formed the league of Mâcon against Charles of Anjou, but the king managed to keep them at peace. The settlement of the claims of the king of England in Aquitaine by the treaty of Amiens in 1279 was a victory for the party of Margaret.

Agenais and southern Saintonge, which fell to the Crown by the death of Alfonse of Poitiers in 1276, as part of his vast possessions in Aquitaine and Languedoc, were ceded to Edward I of England in accordance with the treaty of Paris 1259. Another portion of the heritage of Alfonse, the Venaissin, was ceded to the papacy to redeem an old promise. In general the strong will of Charles of Anjou directed Philip's policy. He secretly urged his nephew's candidature for the imperial crown, left vacant by the death of Richard of Cornwall, king of the Romans, in 1272, but without success. In May 1275 the party of Marie secured for Philip, the king's second son, the hand of Jeanne, the heiress of Navarre and Champagne, along with the guardianship of the kingdom of Navarre during the minority of Jeanne. But early in 1276 Jeanne's mother, Blanche, the widow of Henry III of Navarre and Champagne, married Edmund, first Earl of Lancaster, brother of Edward I; and she and her English husband kept Champagne until, in 1284, Jeanne came of age.

An expedition of Philip against Castile in aid of the children of his sister, Blanche, proved abortive. Regardless of this warning, he was induced in 1284 to take up the quarrel of his uncle Charles in Sicily, after the Sicilian Vespers in 1282. Two assemblies of barons and prelates were held at Bourges in November 1283 and February 1284 to deliberate on the question. This was a mere matter of form; Marie of Brabant and her party had decided the matter beforehand, and the crown of Aragon, which the French pope Martin IV had declared forfeited by Peter, was accepted for Charles of Valois, Philip's third son. The project was strongly opposed by Matthew of Vendôme, who was in correspondence with the king of England on the subject. It was the first warlike expedition undertaken by the house of Capet outside France. It proved a disastrous failure. The French army laid siege to Gerona on the 26th of June 1285. The town surrendered on the 7th of September, but disease and the defeat of the fleet by the Aragonese navy at Las Farmiguas Islands led to a retreat, during which, on the 5th of October, the king died. In the same month the garrison placed at Gerona surrendered. It is typical of Philip's character and career that he should die thus, in an expedition undertaken against the interests of his kingdom, at the instigation of his ambitious uncle.

Philip was twice married. On the 28th of May 1262 he married Isabella, daughter of James I, king of Aragon, who died in 1271. By her he had four children: Louis, who died in 1276; Philip, born in 1268; Charles of Valois, born on the 12th of March 1270; and Robert, who died young. By his second wife, Marie (d. 1322), daughter of Henry III of Brabant, whom he married in 1274, he had three children: Louis, count of Evreux; Margaret, who married in 1299 Edward I, king of England; and Blanche, who married Rudolph III, Duke of Austria.